A liquid crystal display device is provided with a liquid crystal panel unit and a backlight unit disposed on a back surface of the liquid crystal panel unit, and the liquid crystal panel unit adjusts transmittance (amount of transmission) of light from the backlight unit to display an image on a front surface of the liquid crystal panel unit.
The backlight units are roughly classified into two systems. One is a light guide plate system (edge light system) to introduce light from a side surface of a light guide plate, and the other is a direct type system to have a light source on a back surface of a liquid crystal module.
Descriptions are given below to a liquid crystal display device provided with a backlight unit of the edge light system. FIG. 9 is a cross-sectional view of a liquid crystal display device using a backlight unit of a conventional edge light system, and FIG. 10 is an X-X line cross-sectional view of the backlight unit in FIG. 9. As illustrated in FIG. 9, a backlight unit 91 of the edge light system is provided with light source units 93 having a plurality of light sources (LEDs) side by side disposed therein, a light guide plate 92 to receive light emitted from the light source units 93 from light receiving surfaces 922 on side surfaces and to emit planar light from a light emitting surface 921 of one of the main surfaces, an optical sheet 94 disposed adjacent to the light emitting surface 921 of the light guide plate 92. Then, these members are disposed inside housing 97.
As illustrated in FIG. 9, in a liquid crystal display device, a front side pressing member 95 is disposed so as to press front side peripheral portions of the light guide plate 92 and the optical sheet 94 and a liquid crystal panel unit 96 is disposed on a front side of the front side pressing member 95. The planar light emitted from the light emitting surface 921 of the light guide plate 92 is introduced to the liquid crystal panel unit 96, and the liquid crystal panel unit 96 forms a picture by modulating the planar light.
As described above, since an image is formed by modulating planar light in a liquid crystal display device, quality of the image is higher as brilliance of the planar light is higher and uniformity of the brilliance is higher. The light introduced from the light receiving surface 922 is introduced at a large angle of incidence to the light emitting surface 921. When the angle of incidence to the light emitting surface 921 is more than a critical angle, the light is totally reflected on the light emitting surface 921 and the light does not easily emit from the light emitting surface 921, which causes uneven brilliance of the planar light. Therefore, among liquid crystal display devices, those having a concave and convex shape formed in the light emitting surface 921 of the light guide plate 92 are proposed to suppress the uneven brilliance of the planar light and to improve the brilliance on the front side (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-100728 and the like).
In the light guide plate 92, usually, a rising portion is formed on a reflection surface 923 to direct a direction of travel of light inside the light guide plate 92 towards the light emitting surface 921. In the light guide plate 92, by adjusting a shape and (or) density of the rising portion, the brilliance of light towards the light emitting surface 921 is uniformized. A concave and convex shape 924 formed in the light emitting surface 921 acts as a prism, and light transmitting through the concave and convex shape 924 is collected towards the front. This enhances the brilliance of light emitted from the light emitting surface 921.